Thermally stimulated exoelectron emission from hydrogenated amorphous carbon films
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Hydrogenated amorphous carbon ( a - C : H) films on stainless steel (AISI430) substrate oxidized in air at 1273 K were prepared from a gas mixture of methane and hydrogen by an rf plasma chemical vapor deposition, and thermally stimulated exoelectron emission (TSEE) was studied for the x-ray irradiated a - C : H films. Glow curves and energy distributions of TSEE from the 80- and 280-nm a - C :H films and from the AISI430 substrate have been measured under ultrahigh vacuum conditions. It was found that the glow curve from the 80-nm a - C : H film was similar to that from the AISI430 substrate, but it was quite different from that from the 280-nm film; the values of the mean energy of exoelectrons at the glow peak temperatures from the 80-nm a—C: H film are almost the same as those from the substrate but are much lower than those of the 280-nm film. The surfaces of 80- and 280-nm a - C : H films are observed with the scanning electron microscope (SEM). Observations by SEM show that the 80-nm film has relatively large-sized clusters of films and the stainless steel substrate still appears in some places, but the surface of the 280-nm film is completely covered by the carbon films. From these results, we propose that TSEE from the 80-nm film originates mainly from the oxide films on the stainless steel substrate and TSEE from the 280-nm film originates from the film itself. Thus, TSEE can be applied to characterize the surface of thin films.
I. INTRODUCTION
II. EXPERIMENTAL
Hydrogenated amorphous carbon ( a - C : H ) films have recently received attention because of their hardness, optical transparency, and chemical inertness, and surface analysis techniques such as scanning electron microscopy (SEM) and Raman spectroscopy are usually used to characterize the a - C : H films. Exoelectron emission is a surface sensitive phenomenon that conveys valuable information on the surface of the emitter. In the case of thermally stimulated exoelectron emission (TSEE), electron emission intensity as a function of the surface temperature, hereafter called a glow curve, is measured often, and it is found that the glow curve pattern varies with the surface treatment, even in the same material.1 Furthermore, it has been reported that exoelectrons are emitted from the surface layer with depth of approximately 100 nm.2 These results suggest that TSEE may be applied to characterize the surface of a - C : H films which, as far as the authors know, hasn't been done until now. In this paper, the TSEE glow curve and kinetic energy spectrum of exoelectrons from a-C: H films with different thicknesses are described. The glow curve and energy spectrum from the substrate are also measured and compared with those from the a-C: H films. Moreover, the surface of the a-C: H film is observed by SEM, and the relation between the surface characteristics and TSEE is discussed.
Samples of a - C : H films for this study were prepared by an rf plasma chemical vapor deposition from methane and hydrogen mixture gas. The gas mixture was introduced into t
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